I don't know if this is a computer issue or a user error, but in the event that it's a user error, here's an plainest explanation of use I can think of:
Find a vocal part you want to tune. Make a cut on the file at the part before the singer starts singing and make a cut after he stops singing, so it is "isolated". Highlight the isolated region. Click the "Track Pitch" button in AutoTune, and then click the grey "Process" button that all AudioSuite plug-ins have. If your plug-in is working properly, you should now see red squiggly lines representing the pitches of the vocal part you are working on. Select AutoTune's pencil tool, and redraw the sour areas. Now, just like any other AudioSuite plug-in, you can then "Preview" the change, or when you like it, click the "Process" button.
